Sika,
Multi resonance is not a issue. One thing I would like to know is what application are you targeting with this antenna, is it ISM band for Mobile Communication ?(as I can see a resonance at ~2.4 GHz). There are various factors you need to see before designing an antenna.
1) What is the application for the antenna (and hence specifies the constraints for the antenna design). In this case use resonating frequency as reason for antenna operation. Antenna Resonance below -15 dB should be considered.
2) What is the band width of the antenna (for example in Mobile communication you need a antenna with at least 8% band width. here I can see the band width is very low in your case.)
2) What is the Gain, Directivity and Efficiency of antenna in the operating reason. In a microstrip antenna the gain is near to 5-7 dB.
3) What is the Radiation Pattern of the antenna(It should not have big back lobes)
4) What is the Power Radiated by antenna.